The delivery of radio frequency (RF) energy to target regions within solid tissue is known for a variety of purposes of particular interest to the present invention(s). In one particular application, RF energy may be delivered to diseased regions (e.g., tumors) for the purpose of ablating predictable volumes of tissue with minimal patient trauma. RF ablation of tumors is currently performed using one of two core technologies.
The first technology uses a single needle electrode, which when attached to a RF generator, emits RF energy from the exposed, non-insulated portion of the electrode. This energy translates into ion agitation, which is converted into heat and induces cellular death via coagulation necrosis. The second technology utilizes multiple needle electrodes, which have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. In general, a multiple electrode array creates a larger lesion than that created by a single needle electrode.
In theory, RF ablation can be used to sculpt precisely the volume of necrosis to match the extent of the tumor. By varying the power output and the type of electrical waveform, it is possible to control the extent of heating, and thus, the resulting ablation. However, the size of tissue coagulation created from a single electrode, and to a lesser extent a multiple electrode array, has been limited by heat dispersion. As a result, multiple probe insertions must typically be performed in order to ablate the entire tumor. This process considerably increases treatment duration and patent discomfort and requires significant skill for meticulous precision of probe placement. In response to this, the marketplace has attempted to create larger lesions with a single probe insertion. Increasing generator output, however, has been generally unsuccessful for increasing lesion diameter, because an increased wattage is associated with a local increase of temperature to more than 100° C., which induces tissue vaporization and charring. This then increases local tissue impedance, limiting RF deposition, and therefore heat diffusion and associated coagulation necrosis. In addition, patient tolerance appears to be at the maximum using currently available 200W generators.
It has been shown that the introduction of saline into targeted tissue increases the tissue conductivity, thereby creating a larger lesion size. This can be accomplished by injecting the saline into the targeted tissue with a separate syringe. This injection can take place prior to or during the ablation process. See, e.g., Goldberg et al., Saline-Enhanced Radio-Frequency Tissue Ablation in the Treatment of Liver Metastases, Radiology, January 1997, pages 205-210. It has also been shown that, during an ablation procedure, the ablation probe, itself, can be used to perfuse saline (whether actively cooled or not) in order to reduce the local temperature of the tissue, thereby minimizing tissue vaporization and charring. For example, some probes may allow a physician, either before or during the ablation process, to manually inject a specific amount of fluid through the probe, which perfuses out of the needle electrode. These manually performed perfusion processes, however, are imprecise in that the optimum amount of perfusion is difficult to achieve. These perfusion processes also either demand additional attention from the physician performing the ablation procedure or require additional personnel to ensure that enough saline is perfused into the tissue.
One probe, which uses a multiple needle electrode array, can be connected to an injection pump network comprised of several syringes connected in parallel. The syringes are designed to automatically deliver the fluid through the probe and out of the respective needle electrodes, presumably at a prescribed time during the ablation process. While this automated perfusion process does not demand additional attention from the physician, it is imprecise and does not provide dynamic control over the amount of saline perfused into the target tissue, as well as the timing of the saline perfusion.
In addition, when needle electrodes are used to perfuse saline into the target tissue, whether performed manually or automatically, the perfusion exit ports within the needle electrodes often clog as the needle electrodes are introduced through the tissue. As a result, perfusion of the saline is hindered, and thus, the amount of saline perfused into the tissue may be insufficient. Even if the perfusion exit ports within the needle electrode(s) are not clogged, the amount of saline delivered through the needle electrode(s) may be insufficient due to an insufficient number or size of the perfusion exit ports. Also, in the automated perfusion process, additional time and skill is required to set up and connect the pump assembly to the ablation probe, thereby increasing the complexity of the ablation procedure.